Retrieve the previous employee's salary for each employee in the employees table.
CREATE TABLE employees (emp_id INTEGER, salary INTEGER); INSERT INTO employees (emp_id, salary) VALUES (1, 50000), (2, 60000), (3, 55000);
```sql
SELECT emp_id, salary, LAG(salary) OVER (ORDER BY emp_id) AS prev_salary
FROM employees;
```
```sql
SELECT emp_id, salary, LAG(salary) OVER (ORDER BY emp_id) AS prev_salary
FROM employees;
```